In modern surgery, one of the most important instruments available to medical personnel is the powered surgical tool. Often this tool is in the form of a handpiece in which a power generating unit is housed. Power generating units include, electrically driven motors, pneumatically driven motors, ultrasonic vibrators and devices that emit photonic energy (light). An energy applicator extends forward from the handpiece. If the power generating unit is a motor, the energy applicator may be a drill bit, a bur, a saw blade or a reamer. These tools are designed to be used with saw blades or blade cartridges used to separate large sections of hard and soft tissue.
The ability to use a powered surgical tool in a surgical or medical procedure lessens the physical strain of medical practitioners when performing the procedure on a patient. Moreover, most surgical procedures can be performed more quickly and more accurately with powered surgical tools than with the manual equivalents that preceded them.
Integral with the handpiece of many powered surgical tools is a hand switch or trigger. The practitioner using the tool depresses the trigger to actuate the tool power generating unit.
One such trigger switch is a lever arm switch. As implied by the name of this switch, the switch has an elongated body that, at one end, is pivotally attached to the handpiece with which the switch is associated. A spring or other biasing member holds the switch in a static position. The switch is displaced by the practitioner pressing his/her finger against a portion of the switch that is spaced from the location at which the switch is attached to the handpiece. Integral with the switch and/or handpiece is a switch sensor. The switch sensor generates a sensor signal. The sensor varies a characteristic of the sensor signal as a function of the displacement of the switch. Based on the changes in the sensor signal, a control circuit causes energization signals to be applied to the tool power generating unit that results in the actuation of the power generating unit.
The Inventor's Assignee's U.S. Pat. No. 6,017,354 issued 25 Jun. 2000 and its PCT Pat. Pub. No. WO 2013/177423 A2 published 28 Nov. 2013, both of which are explicitly incorporated herein by reference, disclose variations of a trigger switch that can be incorporated into a powered surgical tool. Mounted to the pivoting body of this switch is a magnet. Internal to the body of the handpiece to which the switch is mounted is a sensor. This sensor generates a sensor signal that varies as a function of the variations in the characteristics of the sensed magnetic field. A practitioner uses this type of handpiece by depressing the body of the trigger. This results in a movement of the magnet integral with the trigger body relative to the sensor. The sensor, in turn, outputs a sensor signal that varies as a function of the movement of the trigger magnet relative to the sensor.
A further feature of the above described trigger is that the magnet is moveably mounted to the body of the trigger. The magnet can move between a safety position and a run position. When the magnet is in the safety position, the magnet is positioned relative to the sensor that the magnetic fields emitted by the magnet are, regardless of the position of the trigger, not detectable by the sensor. Only when the magnet is in the run position is the magnet positioned close enough to the sensor actuation of the trigger results in the detectable displacement of the magnet by sensor. In an alternative version of the above assembly a bar is moveably mounted to the trigger body. The bar can be moved to and from a position in which the bar engages the handpiece. When the bar engages the handpiece, the trigger is blocked from displacement.
A benefit of the above design is that when the trigger magnet is in the safety position, the inadvertent depression of the trigger does not result in a like unintended actuation of the tool power generating unit. There is though a possibility that when the practitioner wants to use the tool, the practitioner may inadvertently not remember to move the magnet from the safety position to the run position. If this event occurs, the actuation of the trigger does not result in a like actuation of the tool power generating unit. When this event occurs, the practitioner is required to mentally process the fact that the tool did not respond to the depression of trigger switch. This practitioner is then required to conduct an investigation of the tool to understand that the reason the tool did not respond to the depression of the trigger is that the trigger is in the safety state. Once the cause of the apparent problem is understood, the practitioner moves the magnet from the safety position to the run position. Having to perform these plural distinct mental steps and then the physical step of moving the switch magnet can interrupt the practitioner's thoughts and actions regarding the steps needed to perform the procedure.
In an alternative version of the above assembly a bar is moveably mounted to the trigger body. The bar can be moved to and from a position in which the bar engages the handpiece. When the bar engages the handpiece, the trigger is blocked from displacement. This version of the trigger thus immediately provides the practitioner notice when depressing the trigger, that the trigger is in a safety state.
A limitation of the above assembly is that it has proven difficult to design the assembly so the practitioner, regardless of the hand being used to hold the handpiece can with that hand, both move the trigger in and out of the safety state and depress the trigger.